The present invention relates to electromagnetic interference (EMI) noise mitigation for multi-level power converters.
Switching power converters are often used to convert an alternating current (AC) voltage into a direct current (DC) voltage, or to convert a DC voltage into an AC voltage. Specifically DC to AC converters are commonly used to provide variable frequency and voltage AC power to loads such as AC motors, and AC to DC converters can be used to provide a regulated DC voltage to DC loads. One example of such a power converter is a two-level (2L) converter, which is able to synthesize two node voltages (“levels”) at a phase terminal. These converters typically use pulse-width modulation (PWM) at a fixed switching frequency in order to approximate a desired continuous waveform. PWM is known to cause distortions in the output waveform, which are typically undesirable.
The use of multi-level converter topologies, which synthesize three or more voltages (“levels”), is becoming more prevalent, as these converters are able to produce less distorted waveforms than two-level converters. One multi-level converter topology that synthesizes three node voltages (“levels”) at the phase output is a neutral point clamped three-level converter. This converter uses carrier-based PWM signals with a fixed switching frequency to turn on and off the transistors in each converter phase leg. Although this three-level converter has less distortion than a two-level converter, the use of PWM still causes some distortion in the output waveform.